Rare Daily Staff

Stealth BioTherapeutics presented data from a small, open-label extension portion of the phase 2/3 TAZPOWER study that showed its experimental therapy elamipretide improved heart function in patients with Barth syndrome, an ultra-rare condition characterized by cardiac abnormalities that often lead to heart failure.

In addition to cardiac problems, Barth syndrome causes skeletal muscle weakness, debilitating fatigue, recurrent infections, and delayed growth. Life expectancy is reduced in Barth, with early mortality, including in early childhood, due primarily to heart disease. It occurs almost exclusively in males and is estimated to affect one in 300,000 to 400,000 individuals worldwide at birth. There are currently no FDA-approved therapies for patients with Barth syndrome.

Earlier this month, Alexion Pharmaceuticals agreed to pay Stealth $30 million for an option to co-develop and commercialize elamipretide.

TAZPOWER was a phase 2/3 crossover study of elamipretide in 12 patients with Barth syndrome followed by an open-label extension, in which 10 of the 12 patients participated. In the extension, previously presented as a late-breaker at the 2019 MDA Clinical & Scientific Conference, elamipretide demonstrated potential to improve measures of exercise performance, strength, and patient- and clinician-reported outcomes.

The study results, presented at the American Society of Human Genetics 2019 Annual Meeting in Houston, showed that treatment with elamipretide resulted in a 27 percent increase in the amount of blood pumped by the heart’s left ventricle per contraction, from the trial baseline to week 36 of the open-label extension. Left-ventricular stroke volume is one of the primary determinants of cardiac output, or the volume of blood pumped by the heart, which is an important indicator of how efficiently the heart can meet the body’s demands for perfusion to various organs.

“Based on the data presented showing an increase in stroke volume, treatment with elamipretide appears to have improved heart function, which might indicate cardiac remodeling,” said Reid Thompson, associate professor of pediatrics at the Johns Hopkins University School of Medicine. “Most patients with Barth syndrome have underlying heart disease, so a cardiac effect would be an important outcome in this setting that warrants further investigation.”

The U.S. Food and Drug Administration has granted Fast Track and Orphan Drug designations for elamipretide for the treatment of Barth syndrome.

Photo: Reid Thompson, associate professor of pediatrics at the Johns Hopkins University School of Medicine

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